Integrated low noise amplifier and balun for mri receivers

ABSTRACT

An integrated balun-low noise amplifier (LNA) system is included in a magnetic resonance imaging system. The integrated balun-LNA system conditions electromagnetic signals received from at least one RF receiver coil. The integrated balun-LNA system is configured to be enclosed in a balun housing. The size of the integrated balun-LNA system minimizes component area and volume thereof on or near the RF receiver coil and thus, minimizes interference with the magnetic flux field.

BACKGROUND OF THE INVENTION

The present invention relates generally to receiver electronics in amagnetic resonance imaging (MRI) system, and, more specifically, to anintegrated balun-low noise amplifier (LNA) system.

MRI uses radio frequency pulses and magnetic field gradients applied toa subject in a strong homogenous magnetic field to produce viewableimages. When a substance such as human tissue is subjected to a uniformmagnetic field (polarizing field B₀), the individual magnetic moments ofthe spins in the tissue attempt to align with this polarizing field, butprecess about it, in random order, at their characteristic Larmorfrequency. If the substance, or tissue, is subjected to a magnetic field(excitation field B₁) which is in the x-y plane and which is near theLarmor frequency, the net aligned moment, or “longitudinalmagnetization”, M_(Z), may be rotated, or “tipped”, into the x-y planeto produce a net transverse magnetic moment M_(t). A signal is emittedby the excited spins after the excitation signal B₁ is terminated andthis signal may be received and processed to form an image.

When utilizing these signals to produce images, magnetic field gradients(G_(x), G_(y), and G_(z)) are employed. Typically, the region to beimaged is scanned by a sequence of measurement cycles in which thesegradients vary according to the particular localization method beingused. The resulting set of received MR signals are digitized andprocessed to reconstruct the image using one of many well knownreconstruction techniques.

MR receiver coils receive the electromagnetic signals emitted from thepatient and use the acquired signals for image reconstruction. Beforeimage reconstruction occurs, the electromagnetic signals received by thereceiver coil elements are amplified and filtered to produce an analogsignal that can be further processed into an image. One circuitcomponent in conveying the electrical signal from the receiver coilelement to the analog conversion portion of the receiver is the balun.Typically, these baluns are constructed as stand-alone components. Sucha design can be problematic in that the baluns use large circuitcomponents, that when located in, on, or near the receiver, caninterfere with the magnetic flux field and thus reduce the quality andquantity of signals captured by the receiver. Thus, a balun design thatminimizes the adverse impact of the balun geometry on the image producedby the MRI system would be beneficial.

Another component in the analog conversion chain of the receiver coilelements is the preamplifier. Similar to the balun, the size of thepreamplifier can also interfere with the magnetic flux field and reducethe quality and quantity of signals captured by the receiver. This canbe especially problematic as the quantity of receiver coil elements in aphased array increases and the diameter of the coil elements decreases.The decreased diameter of the coil elements results in a higher densityof coil elements for a fixed receiver geometry, as there is an increasein the ratio of the electronic component volumetric surface area toreceiver coil element area. This increased density of electroniccomponents located near the receiver coil elements effects a higherlikelihood of there being an adverse impact on image quality due to thehigher relative disturbance of the magnetic flux field.

Therefore, a receiver electronics package that minimizes component areaand volume thereof so as to reduce impact on the magnetic field on ornear the receiver coil elements is strongly desired.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to an apparatus and method forintegrating receiver electronics in a magnetic resonance imaging (MRI)system into a single device to overcome the aforementioned drawbacks. Anintegrated balun-LNA system is constructed to be enclosed within astandard balun to minimize volume and impact on the signals acquired bythe RF receiver coils. Such a system would integrate electronic andpassive components and use advanced electronic packaging technologies toachieve this minimization, thereby reducing the impact of the receiverelectronics on image quality.

Therefore, in accordance with one aspect of the present invention, amagnetic resonance imaging (MRI) system includes at least one magnet forgenerating a magnetic field, at least one gradient coil for manipulatingthe magnetic field generated by the at least one magnet by way of agradient field, and at least one RF receiver coil to receiveelectromagnetic signals from the manipulated magnetic field. Alsoincluded in the MRI system is at least one integrated balun-preamplifiersystem configured to condition the received electromagnetic signals,wherein the at least one integrated balun-preamplifier system isenclosed in a balun housing.

In accordance with another aspect of the present invention, anintegrated balun-low noise amplifier (LNA) module includes a balunenclosure, a preamplifier partially located in a first chamber of thebalun housing, and a common-mode inductor located in a second chamber ofthe balun housing, the second chamber also including a remaining portionof the preamplifier. Integrated balun-low noise amplifier (LNA) modulealso includes an internal shield separating the first chamber and thesecond chamber to reduce transmission of magnetic fields between thefirst and second chambers.

In accordance with yet another aspect of the present invention, a methodof constructing an integrated balun-LNA module is set forth. The methodincludes the steps of forming a balun housing, positioning a low-noiseamplifier LNA partially into a first chamber of the balun housing, andpositioning a remaining portion of the low-noise amplifier and acommon-mode inductor into a second chamber of the balun housing. Themethod also includes the steps of positioning an internal shieldingmechanism between the first chamber and the second chamber, positioningan external shielding mechanism at opposing ends of the balun housingand around the balun housing, and electrically connecting the low-noiseamplifier, the balun, the internal shielding, and the externalshielding.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one embodiment presently contemplated forcarrying out the invention.

In the drawings:

FIG. 1 is a schematic of a magnetic resonance imaging (MRI) systemaccording to one embodiment of the present invention.

FIG. 2 is a cross-sectional side view of a balun as known in the priorart

FIG. 3 is a cross-sectional side view of an integrated balun-LNA systemaccording to the present invention.

FIG. 4 is an exploded perspective view of the integrated balun-LNAsystem of FIG. 3.

FIG. 5 is a schematic circuit diagram of the integrated balun-LNA systemof FIG. 3.

FIG. 6 is a detailed cross-sectional side view of a balun shieldaccording to one embodiment of the present invention.

FIG. 7 is an end plan view of the balun shield of FIG. 6.

FIG. 8 is a side cross-sectional view of an additional embodiment of thebalun shield of FIG. 6.

FIG. 9 is a side cross-sectional view of an additional embodiment of thebalun shield of FIG. 6.

FIG. 10 is a side cross-sectional view of an additional embodiment ofthe balun shield of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the major components of a magnetic resonanceimaging (MRI) system 10 incorporating the present invention are shown.This system is merely exemplary and one skilled in the art will readilyunderstand that variations are not only possible, but frequently occurbetween various embodiments. For example, while some components areshown as a separate component, it may very well be incorporated intoanother component.

As shown in FIG. 1, the operation of MRI system 10 is controlled from anoperator console 12 which includes a keyboard or other input device 13,a control panel 14, and a display screen 16. The console 12 communicatesthrough a link 18 with a separate computer system 20 that enables anoperator to control the production and display of images on the displayscreen 16. The computer system 20 includes a number of modules whichcommunicate with each other through a backplane 20 a. These include animage processor module 22, a CPU module 24 and a memory module 26, knownin the art as a frame buffer for storing image data arrays. The computersystem 20 is linked to disk storage 28 and removable storage 30 forstorage of image data and programs, and communicates with a separatesystem control 32 through a high speed serial link 34. The input device13 can include a mouse, joystick, keyboard, track ball, touch activatedscreen, light wand, voice control, or any similar or equivalent inputdevice, and may be used for interactive geometry prescription.

The system control 32 can include a set of modules connected together bya backplane 32 a. These include a CPU module 36 and a pulse generatormodule 38 which connects to the operator console 12 through a seriallink 40. It is through link 40 that the system control 32 receivescommands from the operator to indicate the scan sequence that is to beperformed. The pulse generator module 38 operates the system componentsto carry out the desired scan sequence and produces data which indicatesthe timing, strength and shape of the RF pulses produced, and the timingand length of the data acquisition window. The pulse generator module 38connects to a set of gradient amplifiers 42, to indicate the timing andshape of the gradient pulses that are produced during the scan. Thepulse generator module 38 can also receive patient data from aphysiological acquisition controller 44 that receives signals from anumber of different sensors connected to the patient, such as ECGsignals from electrodes attached to the patient. And finally, the pulsegenerator module 38 connects to a scan room interface circuit 46 whichreceives signals from various sensors associated with the condition ofthe patient and the magnet system. It is also through the scan roominterface circuit 46 that a patient positioning system 48 receivescommands to move the patient to the desired position for the scan. Thepulse generator module 38 may also be located directly in the scan room.

The gradient waveforms produced by the pulse generator module 38 areapplied to the gradient amplifier system 42 having Gx, Gy, and Gzamplifiers. Each gradient amplifier excites a corresponding physicalgradient coil in a gradient coil assembly generally designated 50 toproduce the magnetic field gradients used for spatially encodingacquired signals. The gradient coil assembly 50 forms part of a magnetassembly 52 which includes a polarizing magnet 54 and RF coil 56. Atransceiver module 58 in the system control 32 produces pulses which areamplified by an RF amplifier 60 and coupled to the RF coil 56 by atransmit/receive switch 62. The resulting signals emitted by the excitednuclei in the patient may be sensed by the same RF coil 56 or may bysensed by a separate receiver coil system comprising an array ofmultiple receive coils that are embedded into a structure that is wornby the patient (i.e., a surface coil). The amplified MR signals aredemodulated, filtered, and digitized in the receiver section of thetransceiver 58. The transmit/receive switch 62 is controlled by a signalfrom the pulse generator module 38 to electrically connect the RFamplifier 60 to the RF coils 56 during the transmit mode and to connectthe preamplifier 64 to the coil 56 during the receive mode. Thetransmit/receive switch 62 can also enable a separate RF surface coils(not shown) to be used in either the transmit or receive mode.

One circuit component in conveying the electrical signal from the RFcoils 56 to the analog conversion portion of the receiver is the balun.Shown in FIG. 2 is a balun 65 as is commonly known in the prior art. Asshown, balun 65 is constructed as a stand-alone component. Such a designcan be problematic in that baluns use large circuit components, thatwhen located in, on, or near the RF coils, can interfere with themagnetic flux field and thus reduce the quality and quantity of signalscaptured by the RF coils. Additionally, when the balun 65 is astand-alone component, additional space is required to house a separatepreamplifier.

To maintain the quality and quantity of signals captured by the RF coils56 of FIG. 1 or the surface coils in a receive mode (generally referredto as receiver coils 56 hereinafter), receiver electronics that areconnected to the receiver coils 56 are preferably minimized in volume toreduce interference with the magnetic flux field. That is, as shown inFIG. 3, preamplifier 64 is integrated within balun 66 to form anintegrated balun-preamplifier system 68 or module. Preamplifier 64, asidentified in FIG. 3, includes the input matching inductor 80 as well asamplifier circuitry that is shown in greater detail in FIG. 5.Similarly, balun 66 includes the components of common-mode inductor 69,balun shield 70, and capacitor 94. In a preferred embodiment, thepreamplifier 64 is configured as a low noise amplifier (LNA) 64 thatoperates to amplify the weak electromagnetic signals received by thereceiver coils 56 (shown in FIG. 1), by connecting the LNA 64 directlyinto the received signal. The integrated balun-LNA system/module 68reduces the volumetric impact of the LNA 64 and balun 66 on the magneticflux of signals received by the receiver coils, by reducing the overallvolume of the two components as compared to when each of the balun 66and the LNA 64 are separately housed and electrically connected to thereceiver coils. To achieve this volume reduction, the integratedbalun-LNA system 68 is enclosed within a typical balun 66 (i.e.,enclosed within balun housing 70), with the LNA 64 partly located in afirst chamber 72 thereof and the common-mode inductor 69 and remainderof the LNA 64 located in a second chamber 74 thereof. Separating thefirst chamber 72 from the second chamber 74 is an internal shield 76configured to block feedback induced signals between the first chamberand the second chamber and the circuit therein.

The balun shield 70 is constructed to enclose integratedbalun-preamplifier system 68. Balun shield 70 is constructed of anelectrically conductive rigid tube that includes an end cover/plate 78on each end thereof. The electrically conductive rigid tube preferablyis comprised of a plexiglass tubing surrounded by a copper sleeve,although it is envisioned that other similarly suited materials can alsobe used. Each of the end covers 78 joins with the electricallyconductive rigid tube of balun shield 70 to form an external shield thatfurther blocks feedback induced signals and externally generatedsignals. The end covers 78 also include a miniature electronics package(not shown) thereon that includes printed circuit boards, electroniccomponents, and passive devices, as will be explained in greater detailbelow.

LNA, generally referred to as 64 in FIG. 4, includes input matchinginductor 80 and LNA circuitry, which is shown in greater detail in FIG.5. Referring back to FIG. 4, one component of LNA 64 is field effecttransistor (FET) 100, which is preferably mounted to internal shield 76and located in second chamber 74. Input matching inductor 80 is made upof two separate inductor coils 82, 84. Inductor coils 82, 84 arearranged such that the magnetic flux of inductors 82, 84 is wellcontained inside the volume of the coils. This configuration ensuresminimal variation of the inductance when enclosed by balun shield 70.Input matching inductor 80 provides input matching between the receivercoil 56 of FIG. 1 and an amplifier chip (e.g., PHEMT), and works inconjunction with a capacitor.

Connected to the LNA 64 is common-mode inductor 69 of balun 66, whichfunctions as a passive device in the integrated balun-LNA system 68. Asshown in FIG. 4, common-mode inductor 69 is preferably in the form of acommon mode choke coil made by winding a co-axial cable in the form of acylindrical spiral, the co-axial cable having a non-magnetic core. Thecommon-mode inductor 69 is configured to have a high reactance to theimaging frequency when common-mode currents flow through it and a lowreactance to the imaging frequency when differential-mode currents flowthrough it, and thus, together with the common-mode capacitor 94, formsa parallel resonant circuit that exhibits a high impedance tocommon-mode currents at the imaging frequency, thereby effectivelydecoupling the receiver coils 56 of FIG. 1 from the MRI system 10 bypreventing electromagnetic interference in the analog conversion portionof the transceiver 58, also shown in FIG. 1. Also in a preferredembodiment, the common-mode inductor 69 (i.e., common mode choke coil)is oriented 90 degrees to the input matching inductor coils 82, 84 ofthe LNA 64. Such a construction minimizes mutual magnetic couplingbetween the coils.

Referring still to FIG. 4, the co-axial cable that forms common-modeconductor 69 also forms, in part, signal line 88, along with additionalco-axial cable added thereto. In one embodiment, the signal line 88 isconfigured as a triple-function signal line 88 that transmitselectromagnetic signals into the balun-LNA system 68, powers the LNA 64in one mode, and also provides a bias for a transmit protection circuit90 (shown in FIG. 5) in another mode. Signal line 88 can be composed ofany material suitable for transmitting both power and communicationsignals, although in a preferred embodiment, it is a co-axial cablecomprised of a non-magnetic conductive material.

The functions of the signal line 88 are separated by way of one or morediodes contained in the circuit 96 of the integrated balun-LNA system asshown in FIG. 5. Referring to FIG. 5, an exemplary circuit 96 isdiagrammed for the integrated balun-LNA system of the present invention.As shown therein, diodes 92 are used to separate the power functions ofthe signal line 88 and control power transmission to the LNA. That is,diodes 92 connect the LNA to signal line 88 to power LNA by way of apositive DC voltage and disconnect LNA by way of a negative DC current.Additionally, diodes 92 provide a bias to transmit power to transmitprotection circuit 90 by way of transmit protection bias circuit 89.

The circuit 96 in the integrated balun-LNA system shown in FIG. 5 ispreferably a single 3D component that combines the individual circuitsof the separate balun, preamplifier, and transmit protection biascircuit 89. The integrated circuit 96 is mounted to or integrated withend covers 78 and internal shield 76 of the balun shield 70, shown inFIG. 3, and is minimized by way of flexible printed circuits (patternedmetal on polymide), organic substrates (thin laminate PCBs), electroniccomponents or devices (thin, bare, or packaged ICs), and/or passivedevices (resistors, capacitors, inductors formed within or attached tothe PCBs, etc.). The integrated circuit 96 is designed to allow forpowering of the LNA and transmit protection circuit 90 through thesignal line 88, thus eliminating the need for additional power sourcesor lines.

As shown in FIG. 5, transmit protection circuit 90 is located apart fromthe circuit 96 of the integrated balun-LNA system and is connected bysignal line 88. In this embodiment, the transmit protection circuit 90is located adjacent to the receiver coil 56 shown in FIG. 1.Alternatively, it is also envisioned that transmit protection circuit byincorporated into circuit 96 and into the overall design of theintegrated balun-LNA system 68 shown in FIG. 3. As shown in FIG. 5,transmit protection circuit 90 also contains one or more PIN diodes 98.PIN diode 98 is configured to transmit a negative DC current from signalline 88 to the transmit protection circuit 90 and reduce powerconsumption therein. Rather then implementing a PIN diode 98, it is alsoenvisioned that the transmit protection circuit 90 could implement aMEMS switch, MOSFET, or other MEMS protection device or semiconductorswitch that reduces power consumption and transmits a voltage to thetransmit protection circuit 90.

In another embodiment, it is also envisioned that an energy storagedevice be included in the circuit 96 of the integrated balun-LNA system.In one embodiment, a capacitor can be used to temporarily store energy.The capacitor functions to maintain performance of the integratedbalun-LNA system by reducing interference that can be caused duringswitching in the signal line, as can occur during powering of the LNAand the transmit protection circuit. For example, the capacitor providesa temporary source of power to the LNA to maintain operation thereofduring the transmit protection phase of the signal line operation. As anadditional element, filters can be employed to further help mask thisswitching between the LNA and the transmit protection circuit. While acapacitor has been described for reducing interference during switchingof the signal line powering, it is also envisioned that other suitabledevices can be employed for the same purpose.

Referring back to FIG. 3, other additional components can also be addedto the integrated balun-LNA system 68. In one embodiment of the presentinvention, a Schottky diode 101 is included to disconnect the LNA 64from signal line 88 during a transmit phase.

Beyond any modifications implemented in the circuitry of the integratedbalun-LNA system 68, modifications can also be made to the balun shield70. To further enhance the performance of the balun shield 70, it isenvisioned that a capacitive element can be integrated into the balunshield 70 design. As shown in FIG. 6, end cover 78 of the balun shield70 is constructed as a two conductor parallel plate capacitor 102 that,together with balun shield 70, forms a parallel resonant circuit.Parallel plate capacitor 102 includes an inner conductor plate 104 andan outer conductor plate 106 comprised of a non-magnetic conductivematerial. As one example, conductors 104, 106 comprise aluminumconductors. Between the inner and the outer conductor plates 104, 106 isa dielectric substrate 108 that maintains an electric field between theconductor plates 104, 106. In one embodiment, the dielectric substrate108 is comprised of Kapton, FR4, or a BaTi (barium titanium) basedceramic. It is envisioned, however, that other materials may form thedielectric substrate 108. Inner and outer conductor plates 104, 106adhere to dielectric substrate 108 via, for example, an adhesive orthrough bonding by means such as sputtering of the conductors onto thesubstrate or by thermal bonding.

An additional capacitor unit 130 can be attached to the parallel platecapacitor 102 to increase or tune capacitance in the balun shield 70. Inone embodiment, the capacitor unit 130 is mounted to the inward facingsurface 132 of inner conductor plate 104. A first terminal 134 of thecapacitor unit 130 is attached to the inner conductor plate 104. Asecond terminal 136 of the capacitor unit 130 is connected to the outerconductor plate by way of vias 138 in the parallel plate capacitor 102.Alternatively, the capacitor unit 130 can be mounted to the outwardfacing surface 140 of the outer conductor plate 106. In thisconfiguration, first terminal 134 of the capacitor unit 130 is connectedto the outer plate capacitor 106 and second terminal 136 is connected tothe inner conductor plate 104 by vias 138 through the outer conductorplate 106.

FIG. 7 shows the inner conductor plate 104 and the outer conductor plate106 configured to substantially overlap each other to ensure propershielding to the electrical devices and circuitry contained in the balunshield 70. The overlapping inner and outer conductor plates 104, 106 ofthe parallel plate capacitor 102 provide a reduction in the gap betweenthe end cover 78 and the balun shield 70 that is typically present whena physical resonant capacitor is attached to the end cover 78 of a balunshield 70. In one embodiment, the inner conductor plate 104 isconfigured to be fitted inside the cylindrical balun shield 70. As such,the circumference 110 of the inner conductor plate 104 is sized to besmaller than the circumference 112 of the balun shield 70. Thecircumference 114 of outer conductor plate 106 is constructed to overlapthe circumference 112 of the balun shield 70. In another embodiment, asshown in FIG. 8, outer conductor plate 106 can further include an outerlip 116 that extends axially inward over a small portion of the balunshield 70 to form a cup-like structure that encircles the balun shield70. Such a construction allows the circumference 114 of outer conductorplate 106 to be seam soldered to the circumference 112 of the balunshield 70 to create a solid connection between the end cover 78 and thebalun shield 70 and ensure quality shielding.

As also shown in FIG. 8, the inner conductor plate 104 is furtherconfigured to extend axially inward from the end cover 78. The innerconductor plate 104 includes an inward extending portion 118 that runsalong the circumference thereof to form a cup-shaped inner conductorplate 104. The inner conductor plate 104 fits within the cylindricalbalun shield 70 and extends along an inner surface 120 thereof. Such acup-shaped inner conductor plate 104 allows for additional capacitanceto be added into the overall design of the balun shield 70.

Additional methods and mechanisms are also envisioned to program andadjust desired capacitance into the balun shield 70. In one embodiment,the radius and overall surface area of the inner conductor plate 104 canbe reduced to effect capacitance in the parallel plate capacitor 102. Inan additional embodiment, capacitance of the parallel plate capacitor102 can be programmed by selective patterning and patterninterconnection on the end cover 78 to obtain a desired capacitanceamount. Additional surface mount components can also be mounted to theinner conductor plate 104 to affect capacitance. In yet anotherembodiment, capacitance can be programmed by changing the thickness ofthe dielectric substrate 108 between the inner conductor plate 104 andthe outer conductor plate 106.

Also in one embodiment, parallel plate capacitor 102 is constructed toallow for passage of signal line 88 therethrough. Preferably, the signalline 88 can be guided through the parallel plate capacitor 102 through apassage 128 positioned near the outer circumference of the parallelplate capacitor 102, as shown in FIG. 8. Alternatively, it is envisionedthat signal line 88 can be guided through a passage positioned in thecenter of the parallel plate capacitor 102.

FIG. 9 shows an additional embodiment of the balun shield 70 designwhere a non-magnetic conductive screw 122 is included in the balunshield 70. Non-magnetic conductive screw 122 is inserted axially throughthe parallel plate capacitor 102 and is configured to allow frequencytuning in the balun 66. That is, an operator can adjust the depth ofpenetration of the non-magnetic conductive screw 122 through theparallel plate capacitor 102 and into the interior cavity 124 of thebalun 66 to adjust the inductance of the common-mode inductor 69 (shownin FIG. 4) and enhance the frequency of the balun 66. By tuning thefrequency of the parallel resonant circuit created by the parallel platecapacitor 102 and common-mode inductance to match the imaging frequency,common mode currents of the imaging frequency can be significantlyreduced from propagating down the signal line 88 and degrading thedesired electromagnetic signal. As shown in FIG. 9, in one embodiment,the non-magnetic conductive screw 122 is electrically connected to theouter conductor plate 106 and electrically isolated from the innerconductor plate 104, so as to prevent shorting there between. In analternate embodiment shown in FIG. 10, the non-magnetic conductive screw122 is electrically connected to the inner conductor plate 104 andelectrically isolated from the outer conductor plate 106. The electricalconnection of the non-magnetic conductive screw 122 to either the inneror outer conductor plate 104, 106 allows the balun to resistelectromagnetic field generated disturbances.

To provide mechanical support to the non-magnetic conductive screw 122,a threaded non-magnetic flange 126 can be included in the parallel platecapacitor 102. As shown in FIG. 9, the flange 126 is attached to theouter conductive plate 106 to support the non-magnetic conductive screw122 as it passes through the parallel plate capacitor 102. While theconstruction of the flange 126 and its exact dimensions can vary, it isenvisioned that the flange 126 is able to sufficiently support thenon-magnetic conductive screw 122.

Referring back to FIG. 6, parallel plate capacitor 102 integrated intoend cover 78 is envisioned as being included in balun shield 70 of astandard, stand-alone balun. However, parallel plate capacitor is alsoenvisioned as being included in the end cover of the integratedbalun-LNA system 68 described in detail above and shown in FIGS. 3 and4. Regardless of the exact system it is incorporated with, theintegration of the parallel plate capacitor 102 into the balun shield 70helps to reduce the number of components in the balun and reducemanufacturing steps.

Therefore, in accordance with embodiment of the present invention, amagnetic resonance imaging (MRI) system includes at least one magnet forgenerating a magnetic field, at least one gradient coil for manipulatingthe magnetic field generated by the at least one magnet by way of agradient field, and at least one RF receiver coil to receiveelectromagnetic signals from the manipulated magnetic field. Alsoincluded in the MRI system is at least one integrated balun-preamplifiersystem configured to condition the received electromagnetic signals,wherein the at least one integrated balun-preamplifier system isenclosed in a balun housing.

In accordance with another embodiment of the present invention, anintegrated balun-low noise amplifier (LNA) module includes a balunenclosure, a preamplifier partially located in a first chamber of thebalun housing, and a common-mode inductor located in a second chamber ofthe balun housing, the second chamber also including a remaining portionof the preamplifier. Integrated balun-low noise amplifier (LNA) modulealso includes an internal shield separating the first chamber and thesecond chamber to reduce transmission of magnetic fields between thefirst and second chambers.

In accordance with yet another embodiment of the present invention, amethod of constructing an integrated balun-LNA module is set forth. Themethod includes the steps of forming a balun housing, positioning alow-noise amplifier LNA partially into a first chamber of the balunhousing, and positioning a remaining portion of the low-noise amplifierand a common-mode inductor into a second chamber of the balun housing.The method also includes the steps of positioning an internal shieldingmechanism between the first chamber and the second chamber, positioningan external shielding mechanism at opposing ends of the balun housingand around the balun housing, and electrically connecting the low-noiseamplifier, the balun, the internal shielding, and the externalshielding.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A magnetic resonance imaging (MRI) system comprising: at least onemagnet for generating a magnetic field; at least one gradient coil formanipulating the magnetic field generated by the at least one magnet byway of a gradient field; and at least one RF receiver coil to receiveelectromagnetic signals from the manipulated magnetic field; at leastone integrated balun-preamplifier system configured to condition thereceived electromagnetic signals, said at least one integratedbalun-preamplifier system comprising a low-noise amplifier (LNA) toamplify the received electromagnetic signals and a balun to blockunwanted common mode signals; and wherein the at least one integratedbalun-preamplifier system is enclosed in a balun housing.
 2. (canceled)3. The MRI system of claim 1 wherein the balun further comprises acommon-mode inductor coil and common mode capacitor and the LNA includesan input matching inductor.
 4. The MRI system of claim 3 wherein thecommon-mode inductor coil and the input matching inductor are orientedat 90 degrees to one another to minimize mutual magnetic coupling therebetween.
 5. The MRI system of claim 3 wherein the input matchinginductor is configured to include one of a single input and adifferential input.
 6. The MRI system of claim 3 wherein the balunhousing further comprises: a first chamber to substantially house theLNA; a second chamber to substantially house the common-mode inductorcoil and a remaining part of the LNA; and an internal shield separatingthe first and second chambers.
 7. The MRI system of claim 6 wherein theinternal shield blocks feedback induced signals between the firstchamber and the second chamber.
 8. The MRI system of claim 1 wherein theat least one integrated balun-preamplifier system further comprises anenergy storage device to provide temporary power to the LNA.
 9. The MRIsystem of claim 1 wherein the at least one integrated balun-preamplifiersystem further comprises a transmit protection bias circuit configuredto power a transmit protection circuit.
 10. The MRI system of claim 9wherein the transmit protection circuit further comprises one of a PINdiode, a MOSFET, a MEMS protection device, and a MEMS switch, to reducepower consumption in the transmit protection circuit.
 11. The MRI systemof claim 9 wherein the transmit protection circuit is powered by one ofa negative current and a negative voltage.
 12. The MRI system of claim 9wherein the at least one integrated balun-preamplifier system furthercomprises a signal output configured to transmit the electromagneticsignals, power the LNA, and power the transmit protection circuit. 13.The MRI system of claim 12 wherein the at least one integratedbalun-preamplifier system further comprises at least one diode toselectively transmit power through the signal output to the LNA and thetransmit protection circuit.
 14. The MRI system of claim 12 wherein thesignal output further comprises a co-axial cable.
 15. The MRI system ofclaim 1 wherein the LNA is powered by a positive voltage.
 16. Anintegrated balun-low noise amplifier (LNA) module comprising: a balunenclosure; a preamplifier partially located in a first chamber of thebalun enclosure; a common mode inductor located in a second chamber ofthe balun enclosure, the second chamber also including a remainingportion of the preamplifier; and an internal shield separating the firstchamber and the second chamber to reduce transmission of magnetic andelectric fields between the first and second chambers.
 17. Theintegrated balun-LNA module of claim 16 wherein the integrated balun-LNAmodule conditions electromagnetic signals received from a receiver coilin an MRI system.
 18. The integrated balun-LNA module of claim 17wherein the common mode inductor further comprises a signal lineconfigured to transmit the electromagnetic signals, power thepreamplifier, and power a transmit blocking circuit.
 19. The integratedbalun-LNA module of claim 18 further comprising at least one diode toseparate power transmission through the signal line to the preamplifierand the transmit blocking circuit.
 20. The integrated balun-LNA moduleof claim 18 wherein the transmit blocking circuit further comprises oneof a PIN diode, a MOSFET, a MEMS protection device, and a MEMS switch toreduce power consumption therein.
 21. The integrated balun-LNA module ofclaim 18 wherein the signal line further comprises a co-axial cable toprovide power and transmission of an output data.
 22. A method ofconstructing an integrated balun-low noise amplifier (LNA) module forconditioning electromagnetic signals in an MRI system comprising thesteps of: forming a balun housing positioning a low-noise amplifierpartially into a first chamber of the balun housing; positioning aremaining portion of the low-noise amplifier and a common mode inductorinto a second chamber of the balun housing; positioning an internalshielding mechanism between the first chamber and the second chamber;positioning an external shielding mechanism at opposing ends of thebalun housing and around the balun housing; and electrically connectingthe low-noise amplifier, the common mode inductor, the internalshielding, and the external shielding.
 23. The method of claim 22further including the step of electrically connecting a transmissionprotection circuit.
 24. The method of claim 22 further including thestep of electrically connecting a common-mode capacitor to the externalshielding mechanism.
 25. The MRI system of claim 3 wherein the balunhousing further comprises: a first chamber to substantially house thecommon-mode inductor coil and a portion of the LNA; a second chamber tosubstantially house the remaining portion of the LNA; and an internalshield separating the first and second chambers.